Code:
on $*:TEXT:/^!msg (.+)/iS:#YOUR-CHANNEL-HERE:{
 msg $chan This yo message from $nick :: $regml(1)
 }
You should parenthesize (.+) and then use $regml(1) to refer to what people say. By using $2- , the control codes, be that as color, bold, etc.. won't get stripped.

If $2- is chosen to be used, the /S should have been removed and be made as $strip($2-), but that sorta defeats the purpose of using regex in the first place.

Also, I don't know why the dollar sign has to be used after .+ ; it's not needed.